204 Th e Cytology of Zygnema ericetorum. 
(compare Fig. 1, A and B with Fig. 4, A and B) and the thickness 
of the cell-wall is no greater than is often the case in the terrestrial 
form of Z. ericetorum. The aplanospores of this West Indian form 
were also similar to those of the terrestrial forms of Z. ericetorum 
(compare Fig. 3, A-C with Fig. 4, C-E). The great interest lies in 
the conjugating examples. The conjugation was exactly as in those 
species of Zygnema in which the zygote is lodged in the conjugation- 
canal ( vide Fig. 5) and in no instance was the formation of “ progame- 
tangia ” observed. De Bary’s figures of conjugating Zygogonium 
Fig. 5. Two conjugated examples of Zygnema ericetorum from a warm 
stream in Dominica, W. Indies. X 384. g, empty gametangia ; z, zygospore. 
didymum do not give one the impression of healthy conjugation, but 
rather appear to be abnormalities. It would seem, therefore, that 
the genus “ Zygogonium ” of De Bary is founded upon two abnormal 
examples of conjugation, in consequenceofwhich itcannotbe upheld. 
Moreover, even if De Bary’s contentions were verified and it became 
necessary on account of the conjugation of this alga to place it in 
a genus apart from Zygnema, the name “ Zygogonium” could not 
be used since it would be altogether at variance with Ktitzing’s use 
of it in 1843 and in subsequent works. 
The only characters which separate Zygnema ericetorum from 
the other species of Zygnema are those of the chloroplast, but they 
are not of sufficient importance to warrant the creation of another 
genus for its reception. 
